1. Field of the Invention
The present invention relates to a solid electrolytic capacitor using a conductive polymer compound as a solid electrolyte and a method of manufacturing the solid electrolytic capacitor.
2. Description of the Background Art
In connection with size and weight reductions of electric equipment in recent years, a small capacitor of a large capacity for high frequencies has come to be required. As such a capacitor, a solid electrolytic capacitor using a conductive polymer compound to form a solid electrolyte layer has been proposed.
The solid electrolytic capacitor has a problem of a decrease in adhesion between a dielectric oxide coating, which is formed by oxidation of a surface of an anode body formed with a sintered body of a valve metal such as tantalum, niobium, titanium, or aluminum, and a solid electrolyte layer formed on the dielectric oxide coating, which results in an increased LC (Leaked Current), an increased ESR (Equivalent Series Resistance) and decreased reliability.
To solve the problem, a method for increasing the adhesion between the dielectric oxide coating and the conductive polymer compound layer has been proposed, which includes steps of forming the dielectric oxide coating on the surface of the anode body, treating a surface thereof with a silane coupling agent, and then forming on the surface the conductive polymer compound layer as a solid electrolyte layer to let the silane coupling agent be interposed between the dielectric oxide coating and the conductive polymer compound layer (for example, see Japanese Patent Laying-Open Nos. 02-074021, 04-073924 and 08-293436).
In addition, a method for increasing the adhesion between the dielectric oxide coating formed on a surface of a porous anode body and the conductive polymer compound layer has been proposed, which includes steps of repeating treatment of the dielectric oxide coating with a silane coupling agent and formation of the conductive polymer compound layer to form a first surface treatment layer with the silane coupling agent on the dielectric oxide coating inside the porous body, forming a first conductive polymer compound layer on the first surface treatment layer, forming a second surface treatment layer with the silane coupling agent on the dielectric oxide coating on an outer periphery of the porous body, and forming a second conductive polymer compound layer on the second surface treatment layer (for example, see Japanese Patent Laying-Open No. 11-219860).
Though the adhesion between the dielectric oxide coating and the conductive polymer compound layer is increased while a low ESR is maintained and reliability is increased with each of the methods described above, a capacitance is decreased because of existence of the surface treatment layer with the silane coupling agent (hereafter referred to as a “silane coupling agent treatment layer”) formed between the dielectric oxide coating and the conductive polymer compound layer.